Metal-phenolic networks-engineered polyimide aerogels for high-efficiency gold extraction and separation from e-waste mixture

Engineering adsorption materials that offer easy handling, efficient, and selective recovery of precious metals, such as gold, from electronic waste (e-waste) are of significant interest, especially given the escalating volume of discarded electronic devices. However, the harsh digested solvents (e.g., aqua regia), ultralow gold concentrations (several ppm), and competitive interference from various metals present significant challenges. Herein, we engineer a porous polyimide (PI) aerogel with chemically reductive, mechanically resilient, and environmentally recyclable capabilities, using biomass-derived metal-phenolic networks (MPNs), for highly selective and efficient gold extraction and separation. The resulting aerogels show a high adsorption efficiency (∼97.4 %), selective extraction of gold ions from 12 metal ions in simulated leached solutions, and superior purity (∼100 %) in the reduced gold particles. The gold ions are reduced, nucleate, and grow into large agglomeration (∼12 μm) as observed in experiments and confirmed by density functional theory (DFT) calculations, facilitating their separation from the aerogels without the need for complex processes (e.g., membrane separation). On application to a central processing unit (CPU), our aerogels effectively extracted > 96 % of gold ions even at ultralow concentrations of 3.6 ppm in aqua regia, generating at least 66 times more profit compared to the cost (profit/cost = ∼52.9/∼0.8 $/g). These results demonstrated that MPNs-engineered aerogels are promising economical and practical adsorbents for gold recovery in e-waste.